ABSTRACT
Green tea accounts for approximately 20% of the world’s tea production and for a long time has been the main tea beverage consumed in Japan and parts of China. In recent years, green tea has gained some popularity in other parts of the world. e tea plant, Camellia sinensis, has been cultivated in Asia for thousands of years. Currently, more than two-thirds of the world population consumes this popular beverage. Green tea is rich in tea catechins, namely, epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin (EC), and epicatechin gallate (ECG), which have many cancer chemopreventive properties, including antioxidation, anti-inflammatory, antiproliferative, and antiangiogenic. Catechin, gallocatechin, epigallocatechin digallates, epicatechin digallate, 3-O-methyl EC and EGC, catechin gallate, and gallocatechin gallate are also present in smaller quantities. Catechins are especially concentrated in green tea, which account for 30 to 40% of the dry weight of the leaves. e polyphenolic constituent EGCG is the major and most effective chemopreventive agent in green tea. EGCG appears to be the most powerful of all the catechins, with an antioxidant activity about 25 to 100 times more potent than that of vitamins C and E (Cao et al., 2002). It has been reported that consumption of green tea polyphenols (GTPs) is related to decreased risk or slower progression of cancer of various organs (Khan and Mukhtar, 2010; Khan et al., 2008; Syed et al., 2007a). During manufacturing, green and black teas are processed differently. Freshly harvested leaves are immediately steamed to prevent fermentation, yielding a dry, stable product to produce green tea. is steaming process destroys the enzymes responsible for breaking down the color pigments in the leaves and allows the tea to maintain its green color during the subsequent rolling and drying processes. ese processes preserve natural polyphenols with respect to health-promoting properties. e catechins in green tea are dimerized to form a variety of theaflavins as green tea is fermented to oolong and then to black tea. In this chapter, we discuss the studies of green tea in cell culture, animal models, and humans in the chemoprevention/chemotherapy of cancers of various organs.
